will correct me if I'm completely wrong here, but reference counting isn't all that useful during global destruction. First, how do you figure out which items to collect first? Second, how do you deal with circular references? Third, if everything's going to be cleaned up anyway, does it matter? Fourth, it takes a lot longer to come up with a grand master plan than it does to pick a corner of the pool and start sweeping.
As much as I'd like to believe that you can count on objects being destroyed, during global destruction, in normal, reference-counted order, I've never seen it happen. When it's mattered, I've always had to start the chain reaction myself.